Here's the details for the network we set up for Super Happy Dev House Singapore May 2011
which supported 200+ laptops + phones.

All the wireless devices were set to their lowest power output,
with SSID SHDH for 2.4 GHz and SHDH-5G for 5 GHz.

Should the wireless have failed, we had ~90 wired ports available.
All the NAT / DHCP (30 minute leases) work was done by the apple.
With a bigger venue, the
~250 IP limit of the apple means we'll have to use a different NAT box.

Update: 2011-06-30
It was an airport extreme, not an express that served DHCP.